A thin convex lens of focal length 25 cm has a plane rear surface silvered. Neglect separation. Light traverses the lens twice. Find the effective focal length.
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A thin convex lens of focal length 25 cm has a plane rear surface silvered. Neglect separation. Light traverses the lens twice. Find the effective focal length.

G1 Physics · Accepted Answer

Lens power acts twice; plane mirror adds zero power. F=f/2=12.50 cm.